Charge screening as the key effect governing physical properties of deep eutectic solvents

In this work, we performed all-atom molecular dynamics simulations of the ionic liquids choline chloride (ChCl) and 1-ethyl-3-methylimidazolium chloride, as well as their mixtures with ethylene glycol (ETG) and urea (UR), to obtain deep eutectic solvents (DESs). We calculated the structural and transport properties of all systems studied to explore the differences between pure ILs and DESs. From these results, we discuss the ability of ETG and UR to orient themselves along the ionic electric field, similarly to water in classical electrolytes. This orientational behavior promotes an effective reduction of the electrostatic interactions (usually called "screening" within the context of classical electrolytes). We found that, similar to inorganic salts dissolved in water, the hydrogen-bond donors reduce electrostatic interactions between ions, leading to significant changes in their structural and transport properties.